Sheet-wound coils are often used as low-voltage coils and consequently conduct relatively high currents. The output conductors must therefore be dimensioned accordingly.
When two sheet-wound coils are stacked one on top of the other around a common transformer core with a certain axial space between them, the two sheet-wound coils are identical. However, they are stacked and joined in such a way that, from the winding-direction point of view, they are directed towards each other. This means, therefore, that if a current travels for an instant from the inner layer of one coil to its outer coil, the current from the outer layer of the other coil will continue to the inner layer of the second coil.
It is thus the outer sheet layers of the coils that are joined, i.e., the exterior of the coils. This requires space when electrically dimensioning the main channel to the outer coil. It is therefore of great importance that a joint requires as little space radially as possible.
Coils have previously been joined with the aid of a copper bar in the final turn. If the area of sheet and bar is the same, with a sheet dimension of 0.5.times.1000 mm and bar width of 80 mm, for instance, the bar thickness will be 6.25 mm.